Properties and Structure of Metallurgical Coke...

Properties and Structure of Metallurgical Coke Metallurgical coke is a porous, fissured, silver-black solid and is an important part of the ironmaking process since it provides the carbon (C) and heat required to chemically reduce iron burden in the blast furnace (BF) to produce hot metal (HM). It is a porous C material with high strength produced by carbonization of coals of specific rank or of coal blends at temperatures around 1100 deg C in coke ovens. It is composed of both the organic and inorganic matter. C is the major component of the organic part. Small amounts of sulphur (S), nitrogen (N2), hydrogen (H2) and oxygen (O2) also occur in the organic part. The inorganic matter in coke is called coke ash (mineral matter) and is typically around 12 % on dry basis. Both the organic and inorganic components influence coke reactivity. Thus, coke characterization is an important aspect to understand the quality of coke formed. The basic understanding of coke quality is an important task as it determines the high temperature and gasification behaviours of coke in the blast furnace (BF). As the coke moves towards the lower zones of BF, it degrades and generates fines, which affects the bed permeability and the process efficiency. Hence, superior coke quality is critical for a stable and efficient BF operation. Coke quality is influenced by many factors such as the rank, the maceral composition (leading to isotropic or anisotropic coke structures), the ash composition and the fluidity of the starting coals, the carbonization conditions including peak temperature, heating rate, particle size, pressure and bulk density as well as heat treatment conditions. The important properties of coke, including mechanical strength and reactivity, are governed by the arrangement of the constituent C atoms. The principal features...

Coal Carbonization for Coke Production Dec08

Coal Carbonization for Coke Production...

Coal Carbonization for Coke Production Coal carbonization is the process by which coal is heated and volatile products (liquid and gaseous) are driven off, leaving a solid residue called coke. Carbonization of coal involves heating coal to high temperatures either in the absence of oxygen (O2) or in control quantity of O2. A gaseous by-product referred to as coke oven gas (COG) along with ammonia (NH3), water, and sulphur compounds are also thermally removed from the coal. The coke which remains after this distillation largely consists of carbon (C), in various crystallographic forms, but also contains the thermally modified remains of various minerals which have been in the original coal. These mineral remains, usually referred to as coke ash, do not burn and are left as a residue after the coke is burned. Until recently, the carbonization of coal was considered as ‘destructive distillation’, but with the increased importance of the products of carbonization, this phrase is falling out of use. Now, the coal carbonization is considered to be a physico-chemical process which depends on the coking rate, operating parameters, coal blend properties and the transport of thermal energy. The heating rate of coal influences the strength and the fissuring properties of coke. In order to arrive at a homogeneous quality, the heating of the coal cake in a coke oven is therefore to be uniform over the total length and height of the oven. In addition to this, the plastic layer migration rate influences the level of thermal stress in the re-solidified mass and therefore, the level of fissuring. The coal carbonization process started at the beginning of the 18th century by carbonizing good quality of coking coal in heaps on the ground, which subsequently led to the development of beehive ovens of...

Understanding Blast Furnace Ironmaking with Pulverized Coal Injection Nov04

Understanding Blast Furnace Ironmaking with Pulverized Coal Injection...

Understanding Blast Furnace Ironmaking with Pulverized Coal Injection Injection of pulverized coal in the blast furnace (BF) was initially driven by high oil prices but now the use of pulverized coal injection (PCI) has become a standard practice in the BF operation since it satisfies the requirement of reducing raw material costs, pollution and also satisfies the need to extend the life of ageing coke ovens. The injection of the pulverized coal into the BF results into (i) increase in the productivity of the BF, i.e. the amount of hot metal (HM) produced per day by the BF, (ii) reduce the consumption of the more expensive coking coals by replacing coke with cheaper soft coking or thermal coals, (iii) assist in maintaining furnace stability, (iv) improve the consistency of the quality of the HM and reduce its silicon (Si) content, and (v) reduce greenhouse gas emissions. In addition to these advantages, use of the PCI in the BF has proved to be a powerful tool in the hands of the furnace operator to adjust the thermal condition of the furnace much faster than what is possible by adjusting the burden charge from the top. Pulverized coal has basically two roles in the operation of a BF. It not only provides part of the heat required for reducing the iron ore, but also some of the reducing gases. For understanding the HM production in a BF with the injection of pulverized coal, it is necessary to understand what is happening inside the BF as well as the chemical reactions and the importance of permeability within the furnace and how the raw materials can affect this parameter. The BF is essentially a counter-current moving bed furnace with solids (iron ore, coke and flux), and later molten...

Production of Ferro-Silicon Jun27

Production of Ferro-Silicon...

Production of Ferro-Silicon Ferro-silicon (Fe-Si) is a ferro-alloy having iron (Fe) and silicon (Si) as its main elements. The ferro-alloy normally contains Si in the range of 15 % to 90 %. The usual Si contents in the Fe-Si available in the market are 15 %, 45 %, 65 %, 75 %, and 90 %. The remainder is Fe, with around 2 % of other elements like aluminum (Al) and calcium (Ca). Fe-Si is produced industrially by carbo-thermic reduction of silicon dioxide (SiO2) with carbon (C) in the presence of iron ore, scrap iron, mill scale, or other source of iron. The smelting of Fe-Si is a continuous process carried out in the electric submerged arc furnace (SAF) with the self-baking electrodes. Fe-Si (typical qualities 65%, 75% and 90% silicon) is mainly used during steelmaking and in foundries for the production of C steels, stainless steels as a deoxidizing agent and for the alloying of steel and cast iron. It is also used for the production of silicon steel also called electrical steel. During the production of cast iron, Fe-Si is also used for inoculation of the iron to accelerate graphitization. In arc welding Fe-Si can be found in some electrode coatings. The ideal reduction reaction during the production of Fe-Si silicon is SiO2+2C=Si+2CO. However the real reaction is quite complex due to the different temperature zones inside the SAF. The gas in the hottest zone has a high content of silicon mono oxide (SiO) which is required to be recovered in the outer charge layers if the recovery of Si is to be high. The recovery reactions occur in the outer charge layers where they heat the charge to a very high temperature. The outlet gas form the furnace contains SiO2 which can...

Production of Silico-Manganese in a Submerged Arc Furnace Jun09

Production of Silico-Manganese in a Submerged Arc Furnace...

Production of Silico-Manganese in a Submerged Arc Furnace Silico-manganese (Si-Mn) is an alloy used for adding both silicon (Si) and manganese (Mn) to liquid steel during steelmaking at low carbon (C) content. A standard Si-Mn alloy contains 65 % to 70 % Mn, 15 % to 20 % Si and 1.5 % to 2 % C. Si-Mn alloy grades are medium carbon (MC) and low carbon (LC). The steelmaking industry is the only consumer of this alloy. Use of Si-Mn during steelmaking in place of a mix of high carbon ferro-manganese (Fe-Mn) alloy and ferro-silicon (Fe-Si) alloy is driven by economic considerations. Both Mn and Si are crucial constituents in steelmaking. They are used as deoxidizers, desulphurizers and alloying elements. Si is the primary deoxidizer. Mn is a milder deoxidizer than Si but enhances the effectiveness due to the formation of stable manganese silicates and aluminates. It also serves as desulphurizer. Manganese is used as an alloying element in almost all types of steel. Of particular interest is its modifying effect on the iron-carbon (Fe-C) system by increasing the hardenability of the steel. Si-Mn is produced by carbo-thermic reduction of oxidic raw materials in a three-phase, alternating current (AC), submerged arc furnace (SAF) which is also being used for the production of Fe-Mn. Operation of the process for the Si-Mn production is often more difficult than the Fe-Mn production process since higher process temperature is needed. The common sizes of the SAF used for the production of Si-Mn are normally in the range 9 MVA to 40 MVA producing 45 tons to 220 tons of Si-Mn per day. In the carbo-thermic reduction of oxidic raw materials, heat is just as essential for reduction as C is, due to the endothermic reduction reactions and a...